The invention relates to immunological reagents for diagnostic and therapeutic use in colon and other cancers. In particular, the invention relates to humanized anti-carcinoembryonic antigen ("CEA") monoclonal antibodies ("mAbs") that have the binding affinity characteristics of corresponding mouse anti-CEA mAb (MN14) and the antigenic and effector properties of a human antibody. Further, the invention relates to humanized mabs in which the complementarity determining regions ("CDRs") of an anti-CEA murine mAb is grafted into the framework regions of a human antibody, to DNAs that encode such CDR-grafted antibodies, to vectors and transformed hosts for propagating and expressing the DNAs, and to conjugates of the antibodies useful in diagnostic and therapeutic applications.
A promising approach to cancer diagnosis and therapy involves the use of targeting antibodies to deliver diagnostic and therapeutic agents directly to the site of a malignancy. Over the past decade, a wide variety of tumor-specific antibodies and antibody fragments have been developed, as have methods to conjugate the antibodies to drugs, toxins, radionuclides or other agents, and to administer the conjugates to patients. These efforts have produced great progress, but a variety of largely unanticipated problems have limited the diagnostic and therapeutic utility of some of the reagents thus far developed.
Among the most intractable problems is that which is caused by the human immune system itself, which may respond to the targeting conjugate as a foreign antigen. For instance, patients treated with drugs or radionuclides complexed with murine monoclonal antibodies (which have been the most commonly used targeting antibodies for human) develop circulating human anti-mouse antibodies (HAMAs) and a generalized immediate type-III hypersensitivity reaction to the antibody moiety of the conjugate. Furthermore, even when adverse side effects are minimal (for example, as in a single administration), circulating HAMAs decrease the effective concentration of the targeting agent in the patient and therefore limiting the diagnostic or therapeutic agent from reaching the target site.
Several approaches have been developed to overcome or avoid this problem, with only limited success. One strategy has been to chemically modify the targeting antibody to suppress its antigenicity. For example, conjugation of polyethylene glycol to the targeting antibody (PEGylation) is reported to reduce antigenicity of antibodies. Another approach has been to characterize the situs of antigenicity in an antibody and then remove it. In this vein, Fab', F(ab).sub.2 and other antibody fragments have been used in place of whole IgG. In addition, attempts have been made to reduce the adverse effects of HAMA by plasmaphoretically removing HAMA from blood. Immunosuppressive techniques also have been used to ameliorate the adverse effect of the foreign antibody sufficiently to permit multiple treatments with the targeting agent.
None of these approaches has proven altogether satisfactory. An important need persists for a means to reduce or eliminate the adverse immune response to targeting antibody and antibody conjugates in order to gain the full benefit of these diagnostic and therapeutic agents.
This goal has been achieved with the CDR-grafted humanized murine anti-human CEA mAbs that are described below.